Lithium batteries, which are also known as lithium secondary batteries, have a liquid or gelatinous polyelectrolyte, and generate a current by the migration of lithium ions. Lithium batteries include those provided with positive and negative electrodes formed of active polymers.
Lithium batteries are used as power supplies for personal computers, portable remote terminals, such as pocket telephones and PDAs, video cameras, electric vehicles, industrial robots, artificial satellites and the like, and as energy storage batteries.
The package of the lithium ion battery is a cylindrical or parallelepipedic metal can formed by pressing a metal sheet or a pouch formed by working a packaging laminated structure consisting of a base layer, and an aluminum layer and a sealant layer.
Packages for lithium batteries have the following problems. The metal can has rigid walls and hence the shape of the battery is dependent on that of the metal can. Since the hardware is designed so as to conform to the shape of the battery, the dimensions of the hardware are dependent on the shape of the battery, which reduces the degree of freedom of designing the shape of the hardware.
A package, such as a pouch made from a packaging laminated structure for holding a lithium ion battery module therein or an embossed package formed by pressing a packaging laminated structure, has been developed. Such a package does not place any limit to the degree of freedom of designing the shape of hardware. However, any packaging materials sufficiently satisfactory in physical properties and functions required by packages for lithium batteries have not been developed so far. High moistureproof capability or insulating property is a requisite property of packages. Moistureproof capability is particularly important. A packaging laminated structure for forming a package for a lithium ion battery has, as essential components, a base layer, a barrier layer, and a heat-sealable layer. It is confirmed that adhesion between the layers of the packaging laminated structure affects the requisite properties of a package for a lithium ion battery. If adhesion between the barrier layer and the heat-sealable layer is insufficient, external moisture penetrates a package formed from the packaging laminated structure and holding a lithium ion battery module therein package into the package, the electrolyte of the lithium ion battery module reacts with the moisture to produce hydrofluoric acid. The hydrofluoric acid thus produced corrodes the surface of an aluminum layer serving as the barrier layer to cause the delamination of the barrier layer and the heat-sealable layer. Various means for solving such a problem have been proposed.
When sealing a lithium ion battery module in a package, gaps between the tabs of the lithium ion battery and the package must be securely sealed. However, any measures have been taken to prevent the separation of the package from the tabs due to the corrosion of the surfaces of the tabs. Accordingly, the surfaces of the tabs are corroded gradually in a long time, and the heat-sealable layers or the adhesive films of the package bonded to the tabs separate from the tabs and the sealed system of the lithium ion battery is destroyed.